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Computer Networks Slide 1-1 Reading: pp. 14-19 Learning Objectives: • Computer Networks • The Internet • IP and DNS addresses 2/7/07 Computer Networks • 1 CS120 The Information Era Slide 1-2 Networks allow computers to interconnect for the purpose of sharing data and computing resources o Q1: How do we share data? o Each computer on the network (host) has a name (address) which is used to identify the computer when data is transferred 2/7/07 CS120 The Information Era Computer Network 2 Slide 1-3 http://www.coras-it.co.uk/graphics/network.jpg 2/7/07 CS120 The Information Era 3 1 Local Area Network (LAN) • Slide 1-4 Networks that are geographically close are called Local Area Networks (LANs) o o Inter-office network for a small business Inter-building network • • share documents access a database Q2: Where else may a LAN be used? 2/7/07 4 CS120 The Information Era LAN Server Hard drives database Alice’s Computer Hard drive Switch/Hub Slide 1-5 Backup Device This is called a star network because of its layout Printer Bob’s Computer Hard drive 2/7/07 Q3: What data/resources does this network allow its users to share? Q4: What happens if the switch breaks? Q5: What happens if Bob’s computer breaks? CS120 The Information Era Wide Area Network (WAN) • 5 Slide 1-6 Networks that are geographically distant are called Wide Area Networks (WANs) o Examples? o o each may be a computer or a LAN the WAN may be on top of an existing network • Internet • telephone network 2/7/07 CS120 The Information Era 6 2 The Internet Slide 1-7 • The Internet is a network of networks that are spread all over the world o A network of LANs • Not all LANs are connected to the Internet Q6: Can you give an example of a LAN that you use that is connected to the Internet? Q7: When would you not want your LAN connected to the Internet? 2/7/07 CS120 The Information Era Network Structure • A heterarchical network contains many nodes that are interconnected. o Each node is one computer • A hierarchical network contains a tree-like structure where some nodes are superior to others. 2/7/07 CS120 The Information Era Heterarchical Network 7 Slide 1-8 8 Slide 1-9 Q8: T / F The Internet is a heterarchical structure. Why? 2/7/07 CS120 The Information Era 9 3 Hiearchical Network Slide 1-10 Q9: Give an example of something that is hierarchical. 2/7/07 The Internet • • • 10 CS120 The Information Era Slide 1-11 A characteristic of a heterarchical network is that it is a robust network. If some nodes are removed, data can still be sent between nodes Q10: Hierarchical networks do not lend themselves to robustness. Why? • The Internet also has dynamic routing, where the route of the data is determined at the time of transmission based on current network conditions. • Q11: What current network conditions might affect routing? 2/7/07 CS120 The Information Era Host Machines and Host Names • Each computer on the Internet is a host machine. • Each computer has a unique Internet Protocol address (name), such as 124.110.24.1 o Some computers have a permanent (static) IP address o Some computers have a dynamic address 11 Slide 1-12 Q12: What is the IP address of your lab computer? Q13: What are some computers with static IP addresses? Why? Q14: What are some computers with dynamic IP addresses? Why? 2/7/07 CS120 The Information Era 12 4 Domain Name Servers Slide 1-13 • • But I type www.google.com, not 64.233.167.99! IP address for most hosts are mapped to a Domain Name Service (DNS) address o most often only hosts with static IP addresses o DNS is more more people-friendly • Example DNS Address: mail.yahoo.com o Host Name is: mail o Domain Name is: yahoo.com o more specific, right to left 2/7/07 13 CS120 The Information Era Internet Addresses Slide 1-14 DNS Server www.google.com 64.233.167.99 zeus.cs.pacificu.edu 64.59.233.197 http://www.google.com 64.233.167.99 2/7/07 CS120 The Information Era Host Machines and Host Names • • 14 Slide 1-15 Each domain name consists of: o Site name o Top Level Domain name (TLD) Example: zeus.cs.pacificu.edu o edu refers to an educational site (TLD) o cs is Dept. of Math & Computer Science o pacificu is Pacific University o zeus is a specific machine (host) o domain name: cs.pacificu.edu 2/7/07 CS120 The Information Era 15 5 Host Machines and Host Names • Examples of TLDs include: o .com a commercial organization o .edu a US educational site o .net a network site o .au Australia o .fr France o .hk Hong Kong o .es Spain 2/7/07 CS120 The Information Era Host Machines and Host Names • • • • Slide 1-16 16 Slide 1-17 New TLDs have been added as the original set became overloaded Each machine has a unique IP address o may have multiple DNS addresses (aliases) Anyone can register a DNS address When you type in a DNS address, a domain name server translates it into an IP address. 2/7/07 CS120 The Information Era 17 6